1. Field of the Invention
The present invention relates to a receiving unit of a mobile terminal, and more particularly to an apparatus for suppressing noise using a band-pass filter and a high-pass filter.
2. Description of the Related Art
Recently, a technique for adding a sub-receiving unit to a mobile terminal receiving unit in addition to a main receiving unit is being applied to the mobile terminal receiving unit in order to heighten the performance of the mobile terminal receiving unit.
FIG. 1 is a view illustrating the construction of a diversity system of a mobile terminal having a sub-receiving unit added thereto. Referring to FIG. 1, the diversity system of the mobile terminal includes a transmitting unit 100 and a receiving unit 130 having a main receiving unit 110 and a sub-receiving unit 120.
The transmitting unit 100 includes a mixer 102, an HPF (High-Pass Filter) 104, an LNA (Low-Noise Amplifier) 106 and a high-frequency amplifier 108. The transmitting unit 100 converts a baseband (hereinafter referred to as a “BB”) signal input from a modem of the mobile terminal into a high-frequency signal and outputs the high-frequency signal as a transmitted signal. At this time, a part of the transmitted signal enters into a main antenna 112 and a sub-antenna 122 of the receiving unit 130.
The main receiving unit 110 includes the main antenna 112, a duplexer 114, an LNA 116, an external BPF (Band-Pass Filter) 118 and a mixer 119. The sub-receiving unit 120 includes the sub-antenna 122, two BPFs 124a and 124b, an LNA 126, an HPF 128, and a mixer 129. The received signals input through the main antenna 112 and the sub-antenna 122 are converted into BB signals, and the converted BB signals are input to the modem of the mobile terminal.
As described above, both the main receiving unit 110 and the sub-receiving unit 120 are provided in one chip of the receiving unit 130, and a part of the transmitted signal is input to both the main antenna 112 and the sub-antenna 122. Accordingly, a coupling occurs between a part of the transmitted signal and the received signal in the transmitting unit 100 and the receiving unit 130, and this causes a cross modulation to occur.
Additionally, in the case of the sub-receiving unit 120, two RF (Radio Frequency) SAW (Surface Acoustic Wave) filters are utilized as band-pass filters 124a and 124b, and thus the system cost is increased as the size of the whole system is increased.